Earth-boring tools for forming wellbores in subterranean earth formations may include a plurality of cutting elements secured to a body. For example, fixed-cutter earth-boring rotary drill bits (also referred to as “drag bits”), reamers, back-up cutters, drilling-with casing tools, reaming-with casing tools, and exit mills may include a plurality of cutting elements that are fixedly attached to a body of the tool.
The cutting elements used in such earth-boring tools often include polycrystalline diamond compact (often referred to as “PDC”) cutting elements, which are cutting elements that include a polycrystalline diamond (PCD) material. Such polycrystalline diamond cutting elements are formed by sintering and bonding together relatively small diamond grains or crystals under conditions of high temperature and high pressure in the presence of a catalyst (such as, for example, cobalt, iron, nickel, or alloys and mixtures thereof) to form a layer of polycrystalline diamond material on a cutting element substrate. These processes are often referred to as high temperature/high pressure (or “HTHP”) processes. The cutting element substrate may comprise a cermet material (i.e., a ceramic-metal composite material) such as cobalt-cemented tungsten carbide. In such instances, the cobalt (or other catalyst material) in the cutting element substrate may be drawn into the diamond grains or crystals during sintering and serve as a catalyst material for forming a diamond table from the diamond grains or crystals. In other methods, powdered catalyst material may be mixed with the diamond grains or crystals prior to sintering the grains or crystals together in an HTHP process.
PDC cutting elements commonly have a planar, disc-shaped diamond table on an end surface of a cylindrical cemented carbide substrate. Such a PDC cutting element may be mounted to an earth-boring rotary drag bit or other drilling or reaming tool using fixed PDC cutting elements in a position and orientation that causes a peripheral edge of the diamond table to scrape against and shear away the surface of the formation being cut as the tool is rotated within a wellbore. Other types of cutting elements, such as carbide cutting elements or carbide-covered PDC cutting elements are also used in subterranean drilling operations. It has been found that cutting elements having a cutting face with a surface finish roughness in the range of 0.3 microinch (0.3 μin.) to 2.0 microinches (2.0 μin.) root mean square (RMS), which may be referred to as a “polished” cutting face, exhibit favorable performance characteristics as the cutting element shears formation material from the formation being cut, including, for example, the shearing of formation chips of uniform thickness that slide in a substantially unimpeded manner up the cutting face of the cutting element instead of agglomerating as a mass on the cutting face, accumulating in a fluid course rotationally ahead of the cutting element and potentially causing “balling” of formation material on the tool face, resulting in severe degradation of drilling performance of the rotary drag bit or other drilling or reaming tool.
The drilling action of the tool generates cuttings of subterranean formation material at a cutting edge of the cutting element, which cuttings or “chips” travel on the cutting face of the cutting element toward the evacuation areas of the tool, such as junk slots, and from there to the surface transported by drilling mud.